In the production of semiconductor integrated circuits and other semiconductor articles from semiconductor wafers, it is often necessary to provide multiple metal layers on the wafer to serve as interconnect metallization which electrically connects the various devices on the integrated circuit to one another. Traditionally, aluminum has been used for such interconnects, however, it is now recognized that copper metallization may be preferable.
The semiconductor manufacturing industry has applied copper onto semiconductor wafers by using a "damascene" electroplating process where holes, commonly called "vias", trenches and/or other recesses are formed onto a substrate and filled with copper. In the damascene process, the wafer is first provided with a metallic seed layer which is used to conduct electrical current during a subsequent metal electroplating step. The seed layer is a very thin layer of metal which can be applied using one or more of several processes. For example, the seed layer of metal can be laid down using physical vapor deposition or chemical vapor deposition processes to produce a layer on the order of 1,000 angstroms thick. The seed layer can advantageously be formed of copper, gold, nickel, palladium, or other metals. The seed layer is formed over a surface which is convoluted by the presence of the vias, trenches, or other recessed device features.
A copper layer is then electroplated onto the seed layer in the form of a blanket layer. The blanket layer is plated to an extent which forms an overlying layer, with the goal of providing a copper layer that fills the trenches and vias and extends a certain amount above these features. Such a blanket layer will typically be formed in thicknesses on the order of 10,000 to 15,000 angstroms (1-1.5 microns).
After the blanket layer has been electroplated onto the semiconductor wafer, excess metal material present outside of the vias, trenches, or other recesses is removed. The metal is removed to provide a resulting pattern of metal layer in the semiconductor integrated circuit being formed. The excess plated material can be removed, for example, using chemical mechanical planarization. Chemical mechanical planarization is a processing step which uses the combined action of a chemical removal agent and an abrasive which grinds and polishes the exposed metal surface to remove undesired parts of the metal layer applied in the electroplating step.
The electroplating of the semiconductor wafers takes place in a reactor assembly. In such an assembly an anode electrode is disposed in a plating bath, and the wafer with the seed layer thereon is used as a cathode. Only a lower face of the wafer contacts the surface of the plating bath. The wafer is held by a support system that also conducts the requisite cathode current to the wafer. The support system may comprise conductive fingers that secure the wafer in place and also contact the wafer in order to conduct electrical current for the plating operation.
One embodiment of a reactor assembly is disclosed in U.S. Ser. No. 08/988,333 filed Sep. 30, 1997 entitled "Semiconductor Plating System Workpiece Support Having Workpiece--Engaging Electrodes With Distal Contact Part and Dielectric Cover." FIG. 1 illustrates such an assembly. As illustrated the assembly 10 includes reactor vessel 11 for electroplating a metal, a processing head 12 and an electroplating bowl assembly 14.
As shown in FIG. 1, the electroplating bowl assembly 14 includes a cup assembly 16 which is disposed within a reservoir chamber 18. Cup assembly 16 includes a fluid cup 20 holding the processing fluid for the electroplating process. The cup assembly of the illustrated embodiment also has a depending skirt 26 which extends below a cup bottom 30 and may have flutes open therethrough for fluid communication and release of any gas that might collect as the reservoir chamber fills with liquid. The cup can be made from polypropylene or other suitable material.
A bottom opening in the bottom wall 30 of the cup assembly 16 receives a polypropylene riser tube 34 which is adjustable in height relative thereto by a threaded connection between the bottom wall 30 and the tube 34. A fluid delivery tube 44 is disposed within the riser tube 34. A first end of the delivery tube 44 is secured by a threaded connection 45 to an anode 42. An anode shield 40 is attached to the anode 42 by screws 74. The delivery tube 44 supports the anode within the cup. The fluid delivery tube 44 is secured to the riser tube 34 by a fitting 50. The fitting 50 can accommodate height adjustment of the delivery tube 44 within the riser tube. As such, the connection between the fitting 50 and the riser tube 34 facilitates vertical adjustment of the delivery tube and thus the anode vertical position. The delivery tube 44 can be made from a conductive material, such as titanium, and is used to conduct electrical current to the anode 42 as well as to supply fluid to the cup.
Process fluid is provided to the cup through the delivery tube 44 and proceeds therefrom through fluid outlet openings 56. Plating fluid fills the cup through the openings 56, supplied from a plating fluid pump (not shown).
An upper edge of the cup side wall 60 forms a weir which limits the level of electroplating solution or process fluid within the cup. This level is chosen so that only the bottom surface of the wafer W is contacted by the electroplating solution. Excess solution pours over this top edge into the reservoir chamber 18. The level of fluid in the chamber 18 can be maintained within a desired range for stability of operation by monitoring and controlling the fluid level with sensors and actuators. One configuration includes sensing a high level condition using an appropriate switch 63 and then draining fluid through a drain line controlled by a control valve (not shown). The out flow liquid from chamber 18 can be returned to a suitable reservoir. The liquid can then be treated with additional plating chemicals or other constituents of the plating or other process liquid, and used again.
A diffusion plate 66 is provided above the anode 42 for providing a more controlled distribution of the fluid plating bath across the surface of wafer W. Fluid passages in the form of perforations are provided over all, or a portion of, the diffusion plate 66 to allow fluid communication therethrough. The height of the diffusion plate within the cup assembly is adjustable using threaded diffusion plate height adjustment mechanisms 70.
The anode shield 40 is secured to the underside of the consumable anode 42 using anode shield fasteners 74. The anode shield prevents direct impingement on the anode by the plating solution as the solution passes into the processing chamber. The anode shield 40 and anode shield fasteners 74 can be made from a dielectric material, such as polyvinylidene fluoride or polypropylene. The anode shield serves to electrically isolate and physically protect the backside or the anode. It also reduces the consumption of organic plating liquid additives.
The processing head 12 holds a wafer W for rotation about a vertical axis R within the processing chamber. The processing head 12 includes a rotor assembly having a plurality of wafer-engaging fingers 89 that hold the wafer against holding features of the rotor. Fingers 89 are preferably adapted to conduct current between the wafer and a plating electrical power supply and act as current thieves. portions of the processing head 12 mate with the processing bowl assembly 14 to provide a substantially closed processing volume 13.
The processing head 12 can be supported by a head operator. The head operator can include an upper portion which is adjustable in elevation to allow height adjustment of the processing head. The head operator also can have a head connection shaft which is operable to pivot the head 12 about a horizontal pivot axis. Pivotal action of the processing head using the operator allows the processing head to be placed in an open or faced-up position (not shown) for loading and unloading wafer W.
Processing exhaust gas must be removed from the volume 13. FIGS. 1 and 2 illustrate an outer vessel side wall 76 that extends upwardly from the vessel base plate 75 to a top end into which is nested an intermediate exhaust ring 77 having circumferentially spaced-apart slots 78 therethrough. The slots 78 communicate exhaust gas from inside the vessel 13 to a thin annular plenum 79 located between the intermediate exhaust ring 77 and the outer bowl side wall 76. Surrounding the outer bowl side wall 76 is a vessel ring assembly 80 which forms with the side wall 76 an external, annular collection chamber 81. Gas which is collected in the plenum 79 passes through intermittent orifices 82 and into the annular collection chamber 81. Gas collected in the collection chamber 81 is passed through an exhaust nozzle 83 to be collected and recycled.
The above described apparatus can suffer from some drawbacks. The threaded connection 45 of the anode and the delivery tube may introduce some risk of thread damage during maintenance or installation of a new anode onto the delivery tube. This type of construction also makes the rotational engagement and installation of, or the disengagement and removal of, the anode to/from the delivery tube difficult and time consuming, due to the heavy weight of the anode and the tight clearances between the anode 42 and the cup sidewall 60. The threaded connection requires a sufficient number of anode rotations for a complete threaded engagement during assembly, or complete threaded disengagement during disassembly.
Additionally, in electroplating processes using a consumable anode, it is desired to have an anodic film deposited on a surface of the anode. This film is applied to the anode before wafer processing. However, this anodic film is very fragile and any hand or tool contact with the anodic film during engagement or disengagement is likely to damage the film, which must then be re-grown. This makes the threaded, rotational manipulation and handling of the anode during installation or removal particularly difficult. Also, handling the anode assembly or the diffusion plate during the assembly and disassembly can contaminate surfaces of the anode assembly, the diffusion plate, or other inside surfaces within the volume 13.
The threaded height adjustment of the diffusion plate using threaded height adjustment mechanisms 70 also requires a time consuming operation to precisely install the diffusion plate to the anode. A plurality of securements, such as Allen head screws, are required to be removed to disassemble the diffusion plate from the anode and reinstalled during reassembly. This is an important consideration since the diffusion plate must be removed routinely to inspect anodic film formation on the anode. The adjustment of the plural screw mechanisms can also introduce height and level inaccuracies of the diffusion plate with respect to the anode and/or reactor cup.
Also, the cup assembly located inside the reactor vessel is supported by an adjustable threaded engagement with the riser tube. The threaded engagement may introduce cup height and level misadjustments.
The threaded height adjustment of the anode assembly within the cup, by adjusting the delivery tube, can introduce height and levelness misadjustments. Additionally, the delivery tube being vertically adjustable by loosening of a locking nut located below the reactor vessel, requires access to both the top side of the cup for viewing the anode height adjustment, and the bottom side of the vessel to loosen this locking nut. If the reactor vessel is supported on a deck this requires access to both above and below the deck. Additionally, the delivery tube being vertically adjustable at the reactor vessel base plate requires a more complex seal mechanism between the delivery tube and the anode post at the vessel base plate. Also, the delivery tube serving the dual function of being a liquid conduit and an electrical conductor requires the tube to be constructed of a metallic material which is conductive yet substantially inert to the process chemistry. Such a conduit has been composed of titanium, which is costly.
The present inventors have recognized that it would be advantageous to provide a reactor vessel having an improved connection arrangement between anode and diffusion plate, and between anode and anode support structure to avoid some of the foregoing problems. Further, the inventors have recognized that it would be advantageous to provide a reactor vessel arrangement that facilitates easier assembly and disassembly of diffusion plate, anode, anode support structure and anode electrical conductor than found in the foregoing system. Still further, the present inventors have recognized that it would be advantageous to provide a reactor vessel which eliminates threaded connections to as great a degree as possible.
The inventors have recognized that it would be advantageous to provide a reactor vessel having: an improved mechanical connection arrangement between anode and delivery tube, an improved electrical connection between anode and an outside electrical power source, an improved accessibility for adjusting elements of the reactor vessel, an improved accuracy of vertical adjustment between the anode and the cup, and an improved accuracy of vertical and level adjustment of the cup within the reactor vessel.